Platyhelminthes – Overview, Features, Classification, FAQs

A variety of living organisms exists on this planet which is known as diversity. The organism varies in size, shape, nutrition, reproduction, habitat, and other metabolic activities. On the basis of all these differences, the species are divided into different categories. The classification of all species showing different characters has different classes and orders. There is a variety of environments where animals survive such as desert, water, forest, ice, grasslands, etc. but the characteristics of animals living in different environments are always different. The diversity of animals is seen in different temperatures also like they also survive in high temperatures, cold regions, humid climates, and moisture, environments. This shows that animals have a huge diversity in themselves which needs to classify into different categories so that it becomes easier for us to study and learn about them that’s why the classifications are done which have groups at different levels from top to bottom. One of the reasons for this diversity is DNA. Every species has its own unique DNA which gives that species a different identity. As it is needed to study different forms of life, the first important work is to decide among so many characters which one is the most important and which is least important so that we can arrange them in an order to classify them. Through such analysis, broad groups can be made and under such groups, smaller groups can be created.

Platyhelminthes

In the animal kingdom, there are many different phyla according to their characters and their functions. Here, we will discuss the phylum Platyhelminthes. Approx. there are 13000-20000 species in this phylum. Usually, species in this phylum are known as flatworms or tapeworms as they have flat bodies. Many parasitic life forms are included in this phylum. These are acoelomates as they lack a cavity in their body. Species have different sizes which can vary up to 2-3 feet. The parasites in this phylum are known as blood flukes which have the ability to regenerate themselves. They are invertebrates with soft bodies. There are few species that cause highly damaging diseases in humans. Huge diversity can be seen in this phylum.

Features of Phylum Platyhelminthes

There are many characteristics of this phylum that will help us to understand Platyhelminthes in a better way. They are as follows-

• Firstly, they are parasites and free living.
• The symmetry of the organism in this phylum is bilateral.
• They have three germ layers and are known as triploblastic organisms.
• As they don’t have cavities in them so recognized as acoelomates.
• They lack cilia and have a soft covering over their body.
• Platyhelminthes lack segmentation so no segments can be seen in them and are dorsoventrally flattened.
• They have a mouth for ingestion but the anus is absent and also doesn’t have a circulatory system.
• Respiration is done by the body surface through simple diffusion.
• The organization level is seen in this phylum.
• The digestive system is absent in Platyhelminthes.
• In the same body, both male and female organ is present that’s why they are called to be hermaphrodites.
• Both modes of reproduction are used in this phylum. Sexually they reproduce by fusion of gametes and by asexually they reproduce by fission and regeneration.
• Internal fertilization is seen in this phylum.
• One too many larval stages are seen in their life cycles.
• For excretion and osmoregulation, they have flame cells.
• In a ladder-like fashion, they have nerve cords that comprise the nerve system and brain.
• Transportation of food is done by the fluid and connective tissues present in the space between body walls and organs.

Distinguishing features of Phylum Platyhelminthes

Every phylum has some special or different characteristics which differentiate them from other phyla. Some of the unique features that Platyhelminthes exhibits are as follows-

• For excretion, only Platyhelminthes have flame cells.
• The nervous system is ladder-like which is not seen in any other phylum.
• Fertilization is done by themselves only. 
• The body cavity of Platyhelminthes has connective tissues which are a unique feature of this phylum.

Classification of Platyhelminthes

Platyhelminthes are divided into three classes

Turbellaria

• Mostly found in fresh water and these are free-living organisms.
• The body is flat dorsoventrally.
• Suckers and hooks are absent in this class.
• For example, Planaria, Otoplana, etc.

Trematoda

• All the species are mostly parasitic.
• Suckers and hooks are usually present
• For example Diplozoon, Fasciola, Hepatica, etc.

Cestoda

• Hooks and suckers are present in this class.
• Only parasites are included in this class.

Frequently Asked Questions

Question 1: Explain the excretory system of Platyhelminthes.

Answer: 

Specialized organs which are used for excretion are flame cells. The function of these flames cells is similar to kidney, removal of waste products. There are other organs present in other organisms which have the same function as kidney like malpighian tubules which is tubular excretory organs present in the gut of insects.

Question 2: What is the common name of Platyhelminthes and what is the reason behind that name?

Answer:

Usually, they are known by many names like flatworms or tapeworms. The reason behind these names is that they have a soft covering over their body and are flat in shape. Moreover, they are parasitic in nature and found as parasites in humans. Some of them are free-living also.

Question 3: List the special features which are only seen in Platyhelminthes?

Answer:

Every phylum has some distinguishing features which specify its identity among other phyla. Platyhelminthes also have such features that are-

1. Their body shape is dorsoventrally flattened.
2. Cover of ciliated epithelium over their body.
3. The absence of a cavity makes them acoelomate.
4. They just have one sac-like digestive cavity used for digestion.
5. Presence of flame cells for excretion.

Question 4: What is the disease caused by Taenia solium?

Answer:

The disease caused by Taenia solium is called taeniasis. The symptoms of this disease are abdominal pain, false appetite, restlessness, and indigestion. Its larva is in pigs but the rest lives in the small intestines of humans. These types of diseases are lethal for humans.

Question 5: What are the basic systems that are absent in Platyhelminthes?

Answer:

There are many systems that are not well developed in Platyhelminthes that are digestive systems in which the alimentary canal is absent but they have a sac-like structure for digestion. Moreover, they lack a circulatory system and the circulation is done by an open system. For respiration, they lack a proper respiratory system and respiration occurs through diffusion through body surface.

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